Adjustable camshafts serve the purpose of a variable valve train of an internal combustion engine, and the phase position of the inner shaft can be adjusted relative to the phase position of the outer shaft by the phase shifter during rotation of the adjustable camshaft. It is also possible to adjust the phase position of the inner shaft and the outer shaft jointly relative to the phase position of a drive wheel, via which drive wheel the camshaft is driven rotationally about the axis of rotation. What are known as dual phase shifters enable, for example, the change of the phase position of the outer shaft and the inner shaft jointly and adjustment of the phase position of the inner shaft relative to the outer shaft is simultaneously possible.
Phase shifters are generally operated by a pressurizing medium, in particular an oil, in that pressure chambers formed between a rotor and a stator of the phase shifter are alternately acted upon fluidically. In order to enable the supply of pressurizing medium to the phase shifter which rotates with the camshaft, supply with the pressurizing medium is generally carried out via a bearing portion on the outer shaft of the camshaft, via which bearing portion the camshaft is mounted in a bearing bridge. The bearing portion generally forms the outermost bearing portion at the end of the camshaft so that the outer shaft and in particular the inner shaft terminate with the bearing portion in their longitudinal direction along the axis of rotation and wherein the phase shifter adjoins the end in the direction of the axis of rotation. The rotor is generally fastened at the end of the inner shaft and the stator of the phase shifter is generally fastened at the end of the outer shaft. Particularly in the case of dual phase shifters, the problem arises that, for example, four or more ducts are necessary in order to load the individual chambers between rotor and stator of the phase shifter with pressurizing medium. If the phase shifter, in particular the rotor, is fastened with a central screw on the inner shaft, particular difficulties arise when accommodating the ducts in the inner shaft and/or the outer shaft as a result of the reduced installation space.
For example, DE 10 2006 028 611 A1 shows an adjustable camshaft with a phase shifter which is screwed at the end side on the inner shaft with a central screw. The outer shaft is received rotatably in a bearing ring, wherein the bearing ring is formed to co-rotate with the outer shaft. The bearing ring is received in an abutment which is formed by the bearing bridge, for example, of the camshaft module or the like and does not co-rotate. Only two oil ducts are represented which are guided on the actuating elements of the phase shifter and which must run via the end-side bearing portion of the camshaft. Further oil ducts are guided via a bearing portion and run centrally through the inner shaft and through a gap between the inner shaft and the outer shaft. It is, however, desirable here to limit the fluid supply of the phase shifter to the end-side bearing portion which is located close to the phase shifter on the camshaft.
A further adjustable camshaft is known from DE 10 2006 013 829 A1, and the inner shaft of the camshaft comprises a threaded bore into which a central screw can be screwed in order to fasten the phase shifter on the camshaft. The accommodation of the oil ducts must consequently be provided on the radial region between the threaded bore and the receiver of the fastening flange which sits on the end side on the outer shaft. The arrangement of a dual phase shifter is, for example, already not readily possible as a result of the restricted space conditions for accommodation of the oil ducts.